oil smell coming from vents

[rattler64]

I noticed someone posted a thread about having an oil smell coming from their vents after they had their oil changed. I think it was posted in the 6.0 tech files forum. I have the same problem and was wondering if they found the cause. I have an 04 F250 6.0L, bought it with about 104,000 miles on it, all stock, previous owner was running MC and I changed to T5. Noticed the smell right after changing oil, drove it about 2500 miles and it went away, changed the oil again and started getting the smell again. it comes from the vents only at a stop and idling. Checked the oil sensor on top of the engine near the filter and that looks like its not leaking. Any suggestions? thanks